While remote indication of appliance status is well-known, as well as the signalling of appliance status over internal AC wiring of a dwelling, prior signalling systems do not address the problem of multiple remote indicating modules or the problem of providing parallel indications to one group of remote modules, while excluding another group of remote modules.
The problem of multiple indicators arises in the apartment house or condominium context in which a number of individual apartment or condominium units share the use of a single washing machine, dryer, or other appliance. As is often the case in large apartment complexes a washing machine or dryer is provided for each floor of the complex. Because there are not enough washing machines to match the number of units on the floor, there is a necessity for providing each unit on the floor with an indication as to whether the machine is in use or not, so as to save the occupant a useless trip to the machine.
Prior art remote appliance status systems such as illustrated in U.S. Pat. No. 4,916,439, 3,842,408; 3,594,784; and 3,334,340 are all limited to a single indicator for use in determining the in-use status of the appliance.
As such, they are not readily adaptable multi-unit complexes. Moreover, none of the above patents, save U.S. Pat. No. 4,916,439 teach a simple method for determining the status of an appliance by externally sensing the current of the appliance outside of the case or housing of the appliance.
Moreover, it will be appreciated that in order to provide a universal indication system applicable to different manufacturers, it is important to be able to retrofit appliances without having to rewire the appliance.
The aforementioned U.S. Pat. No. 4,916,439 solves this problem by providing a current detector for detecting by the amount of current drawn, whether or not a load has been coupled to the AC line, and thus whether the machine is in use. However, in this system the output of the current detector is coupled to an RF transmitter for radioing the status via an RF link to a single remote indicator. No attempt is made in this system to transmit appliance status information over AC lines, much less to multiple remote indicators.
There is thus a need for a simple, easily retrofitable system for providing a multi-unit dwelling with the ability for the occupants to know when a commonly shared appliance is in use. It is also important that when more than one appliance is provided, the status of this appliance be provided only to a limited group of users even though common AC wiring of the dwelling is used.